The present invention relates to friction clutches in general, and more particularly to improvements in diaphragm springs which are utilized in friction clutches, especially in friction clutches for transmission of torque between the engine and the change-speed transmission of a motor vehicle.
As a rule, the diaphragm spring of a friction clutch for use in motor vehicles or the like comprises a ring-shaped main section and a set of radially inwardly extending prongs or fingers which are separated from each other by slots and whose free end portions or tips define a centrally located opening. The diaphragm spring is tiltably mounted on a support, e.g., on the housing or cover of the friction clutch, and bears against a pressure plate so as to urge the latter axially toward engagement with the friction linings of a clutch disc. The pressure plate is driven by the crankshaft and the clutch disc transmits torque to the input shaft of the change-speed transmission if the friction clutch is installed in a motor vehicle.
The trend in the automobile industry is toward the making of high-performance lightweight and compact vehicles. This involves a reduction of the weight and space requirements of practically all components including the friction clutch. Thus, the working capacity of the clutch should be increased, and such increase should take place simultaneously with a reduction in dimensions and weight. Since the manufacturer of a friction clutch does not have too much freedom in the selection of materials for component parts of the friction clutch (rather narrow limits are imposed by the cost of raw materials as well as by the ability of materials to be treated in an economical way). One of the important parameters of a satisfactory friction clutch for use in motor vehicles is its ability to stand pronounced thermal stresses for extended intervals of time and/or to dissipate heat before the elevated temperatures could adversely affect sensitive friction linings and certain other heat-sensitive parts. The operating temperature of a modern compact engine for motor vehicles is sufficiently high to greatly reduce the useful life of friction linings and/or to cause undesirable and pronounced thermally induced distortion of the cover, pressure plate, clutch disc and/or other parts of the friction clutch. Therefore, rapid dissipation of friction-induced heat in a friction clutch is of utmost importance.
German Utility Model No. 66 06 711 proposes to provide the diaphragm spring of a friction clutch with openings in the region of slots between the prongs. The openings are supposed to allow for circulation of air and attendant cooling of the friction clutch. The dimensions of such openings cannot be increased at will because this would entail undue weakening of the spring. Furthermore, and in the absence of any additional undertakings, mere provision of openings in the prongs contributes little, if anything, to the dissipation of heat.
U.S. Pat. No. 3,417,846 proposes to provide bent-over portions at one or both sides of each prong of the diaphragm spring. The purpose of such configuration of the prongs is to reduce the lift-off losses which develop as a result of bending of the prongs. The bent-over portions are supposed to reinforce the prongs and to thus ensure predictable disengagement of the clutch while minimizing the distance which the prongs must cover in order to effect a disengagement of the pressure plate from the adjacent linings of the clutch disc.